[QGIS-Developer] Some initial OpenCL feedback

[Alessandro Pasotti]

On Tue, Sep 4, 2018 at 4:57 PM Andreas Neumann <a.neumann at carto.net> wrote:

> Hi Alessandro,
>
> Thanks for the clarification that only the change of the OpenCL-device
> needs a restart.
>
> I tried both - acceleration in CPU and in GPU. I had the impression that
> the acceleration in the CPU was slightly faster than in the CPU - but not a
> lot faster. Maybe the GPU (Intel HD Graphics 4600) is not too powerful. It
> is a ThinkPad notebook, not a desktop.
>

Thanks for the info!

Yes, maybe that the lower I/O (there is no need to transfer data to/from
the graphic card) compensates the slower processing on the CPU

Cheers

Greetings,
>
> Andreas
>
> On 2018-09-04 15:56, Alessandro Pasotti wrote:
>
>
> On Tue, Sep 4, 2018 at 2:21 PM Andreas Neumann <a.neumann at carto.net>
> wrote:
>
>> Hi Alessandro,
>>
>> I just tested if the hardware acceleration (OpenCL) helps in the live
>> hillshade renderer.
>>
>
>
> Hi Andreas,
>
> thanks a lot for your feedback, I honestly am a little worried about the
> possible problems on different platforms, graphic cards and driver
> versions, I choose to stay on the safe side and there is a safeguard that
> disables the OpenCL support at the first issue in the renderer.
>
> The processing algs looks generally more stable (never got a single crash
> myself).
>
>
>
>> The good news is that it works stable so far and substantially improves
>> rendering time of the live hillshade renderer. My notebook on my workplace
>> is rather slow. Without hardware acceleration it renders the hillshade in
>> approx 8 seconds (large window on two screens). With OpenCL acceleration
>> set to on, it renders in about 1 second or even less. I assume quite some
>> time is also spent on reading the file. This with resampling on (average
>> for zooming out and bilinear for zooming in beyond native resolution).
>>
>
> Yes some time is spent on reading the file and some time is spend on I/O
> tranferring data to/from the graphic card, this means that the performance
> gain is usually higher on larger images than on smaller images.
>
>
>> Hardware is an Intel HD Graphics 4600. The CPU is also listed as
>> supported.
>>
>
> Can you also try the CPU? I'm curious about the performances.
>
>
>> Visually, with or without HW accelation on, there still are some
>> rectangular artefacts in both versions.
>>
>
> Yes: that does not change, the algorithm is pretty much the same in both
> implementations.
>
>
>
>> Tested on Windows.
>>
>> --------------
>>
>> One more thing: on my machine there is no restart of QGIS necessary for
>> the changes (HW acceleration on of off) to be applied. This is contrary to
>> the statement in the settings dialogue, which says, that a restart of QGIS
>> is necessary.
>>
>
> The text can probably be improved: what needs a restart is if you change
> the device, enabling and disabling OpenCL support does not require a
> restart.
>
>
>> ---------------
>>
>> Thanks a lot for your work!
>>
>
>
> Thank you for the feedback!
>
>
>
>
> --
> Alessandro Pasotti
> w3:   www.itopen.it
>
>
>

-- 
Alessandro Pasotti
w3:   www.itopen.it
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